Hand-held vacuum and pressure pumps are generally useful whenever vacuum or pressure is desired. Vacuum or pressure can be created, for example, by compressing (i.e. squeezing) and releasing a handle of such a vacuum or pressure pump. Generally, such squeezing and releasing causes a piston to move in a cylinder of the pump thereby creating vacuum or pressure.
Such hand-held vacuum and pressure pumps are especially useful for various tasks such as aiding in performing vacuum extractions during childbirth, and are useful in various industries, such as the automotive industry, for liquid sampling and vacuum system testing and repair.
Since hand-held vacuum pumps are generally operated by one hand, it has been necessary in many cases to use the operator's second hand to operate a vacuum release valve. As will be appreciated, this can be cumbersome, especially when operating a vacuum release valve in a confined environment with limited maneuverability, where there may be fluids or lubricants present, or when there are time restrictions or psychological pressures. Furthermore, it may be desirable to limit the release of the vacuum in a controlled manner, and with minimal finger pressure and dexterity.
The above-referenced U.S. Pat. Nos. 4,806,084 and 5,112,203 describe and disclose vacuum release valves. The '084 patent describes a relatively simple vacuum release valve attached to a vacuum pump which can be released relatively easily by a finger of the same hand that is operating the pump. However, for some applications, the '084 vacuum release valve may release the vacuum too quickly or require greater dexterity than possessed by the operator. Moreover, use of the '084 vacuum release valve could be cumbersome in that the release is not biased to either the "closed" or the "open" position. Hence, the operator might become frustrated in unsuccessfully attempting to draw a vacuum when the vacuum release valve is set to the "open" position.
The '203 patent describes a vacuum release valve which is attached to a vessel in which a vacuum is drawn, and where the vacuum release valve is biased to a closed position. Furthermore, the vacuum release valve described can release a vacuum relatively easily in response to finger pressure. However, for some applications, the '203 vacuum release valve may not be optimal because the mechanism is attached to the vessel in which a vacuum is drawn and not to the vacuum pump itself. In addition, although the rate of flow of air entering and exiting the vacuum may be customized, it is done so by altering the physical size of the passageways in the plunger.
It would be beneficial to have a release mechanism which allows a variety of release rates without the necessity of changing the physical features of the mechanism.